Device and method for selectively removing a thrombus filter

ABSTRACT

A thrombus filter which can be securely fixed in a selected location in the vascular system of a patient and removed when no longer required. The thrombus filter includes a plurality of struts which radiate from a body portion to form the generally conical shape of the thrombus filter. The thrombus filter includes anchor members joined to the free end of each strut. The thrombus filter includes an insulating layer substantially covering the thrombus filter including the body portion, the struts and the anchor members. The insulating layer includes an opening proximate the anchor members. The opening in the insulating layer creates a conductive path between the thrombus filter and the patient&#39;s body. When removal of the thrombus filter is desired, a first electrical conductor forms an electrical connection with the body portion of the thrombus filter. A second electrical conductor forms an electrical connection with the patient&#39;s body. A power supply is used to selectively apply a voltage differential between the thrombus filter and the body of the patient. This voltage differential induces an electrical current the flow of electrical current between the thrombus filter and the patient&#39;s blood causes the electrolytic corrosion of the thrombus filter proximate the opening in the insulating layer. When the bond between the struts of the thrombus filter and the anchors is cut through or weakened, the thrombus filter may be pulled into the lumen of a retrieval catheter. Removal of the thrombus filter from the patient&#39;s body is completed by withdrawing the retrieval catheter from the patient&#39;s blood vessel.

FIELD OF THE INVENTION

[0001] The present invention relates generally to filters for use insideblood vessels. More particularly, the present invention relates tothrombus filters which can be securely affixed at a selected location inthe vascular system and removed when no longer required.

BACKGROUND OF THE INVENTION

[0002] There are a number of situations in the practice of medicine whenit becomes desirable for a physician to place a filter in the vascularsystem of a patient. One of the most common applications for vascularfilters is the treatment of Deep Venous Thrombosis (DVT). Deep VenousThrombosis patients experience clotting of blood in the large veins ofthe lower portions of the body. These patients are constantly at risk ofa clot breaking free and traveling via the inferior vena cava to theheart and lungs. This process is known as pulmonary embolization.Pulmonary embolization can frequently be fatal, for example when a largeblood clot interferes with the life-sustaining pumping action of theheart. If a blood clot passes through the heart it will be pumped intothe lungs and may cause a blockage in the pulmonary arteries. A blockageof this type in the lungs will interfere with the oxygenation of theblood causing shock or death.

[0003] Pulmonary embolization may be successfully prevented by theappropriate placement of a thrombus filter in the vascular system of apatient's body. Placement of the filter may be accomplished byperforming a laparotomy with the patient under general anesthesia.However, intravenous insertion is often the preferred method of placinga thrombus filter in a patient's vascular system.

[0004] Intravenous insertion of a thrombus filter is less invasive andit requires only a local anesthetic. In this procedure, the thrombusfilter is collapsed within a delivery catheter. The delivery catheter isintroduced into the patients vascular system at a point which isconvenient to the physician. The delivery catheter is then fed furtherinto the vascular system until it reaches a desirable location forfilter placement. The thrombus filter is then released into the bloodvessel from the delivery catheter.

[0005] In the treatment of Deep Venous Thrombosis, a thrombus filter isplaced in the inferior vena cava of a patient. The inferior vena cava isa large vessel which returns blood to the heart from the lower part ofthe body. The inferior vena cava may be accessed through the patient'sfemoral vein.

[0006] Thrombus filters may be placed in other locations when treatingother conditions. For example, if blood clots are expected to approachthe heart and lungs from the upper portion of the body, a thrombusfilter may be positioned in the superior-vena cava. The superior venacava is a large vessel which returns blood to the heart from the upperpart of the body. The superior vena cava may by accessed through thejugular vein, located in the patient's neck.

[0007] Once placed inside a blood vessel, a thrombus filter acts tocatch and hold blood clots. The flow of blood around the captured clotsallows the body's lysing process to dissolve the clots.

[0008] The walls of the blood vessels are lined with a thin innermembrane or intima. When the anchor portions of a thrombus filterpuncture this inner membrane the body responds in a process referred toas neointimal hyperplasia. As a result, the punctured area of innermembrane is overgrown with a number of new cells. The anchor portions ofthe thrombus filter are encapsulated with new cell growth (neointimalhyperplasia).

[0009] Due to neointimal hyperplasia, thrombus filters placed in theblood vessel of a patient become affixed in the blood vessel wallswithin two weeks after being implanted. Because the portions of thefilter contacting the blood vessel wall become fixed in this way, manyprior art filters cannot be removed percutaneously after being in placefor more than two weeks.

SUMMARY OF THE INVENTION

[0010] The present invention pertains to a thrombus filter and a methodof removing a thrombus filter using minimally invasive methods whilelimiting complications due to neointimal encapsulation of the anchorportions of the thrombus filter. A thrombus filter for use with theinventive removal method includes a body member and a plurality ofelongated struts. Each strut has a joined end and a free end. The joinedend of each strut is fixably attached to the body member on the thrombusfilter. The struts radiate outwardly from the body member of thethrombus filter such that the thrombus filter is generally conical inshape. A thrombus filter includes an insulating layer substantiallycovering the thrombus filter including the body portion, struts, andanchor members. The insulation layer includes an opening. In oneembodiment of the current invention, the opening in the insulation layeris proximate a sacrificial link. The opening in the insulation layerallows direct contact between a portion of the thrombus filter and thepatient's blood. This direct contact creates a conductor path betweenthe thrombus filter and the body of the patient.

[0011] When removal of a thrombus filter is desired, a first electricalconductor forms an electrical connection with the body portion of thethrombus filter. A second electrical connector forms an electricalconnection with the patient's body. A power supply is used toselectively apply a voltage differential between the body portion of thethrombus filter and the body of a patient. This voltage differentialinduces a current through the thrombus filter.

[0012] When a voltage differential is applied between the body portionof the thrombus filter and the body of a patient, current flows betweenthe thrombus filter and the patient's blood at a location proximate theopening in the insulating layer. The flow of electrical current betweenthe thrombus filter and the patient's blood causes electrolyticcorrosion of the thrombus filter in a selected area. The current flow iscontinued until a selected area of the thrombus filter has been weakenedor cut through by electrolytic corrosion. In one embodiment of thethrombus filter, electrolytic corrosion weakens or cuts through asacrificial link holding an anchor to the thrombus filter.

[0013] When the thrombus filter is deployed inside a blood vessel, thefree ends of the struts engage the blood vessel wall. The body member ofthe thrombus filter is held in a position proximate the center of theblood vessel by the plurality of struts which engage the blood vesselwalls with opposing force vectors. The conical formation of struts actsto trap or capture blood clots. The generally conical shape of theformation of struts, serves to urge captured blood clots toward thecenter of the blood flow. The flow of blood around the captured bloodclots allows the body's natural lysing process to dissolve the clots.

[0014] To assure firm attachment of the thrombus filter to the bloodvessel, anchor members may be attached to the free ends of the struts.In one embodiment of the thrombus filter, anchors are attached by asleeve. In a second embodiment of the thrombus filter, anchor membersare attached by a sacrificial link. In a third embodiment of thethrombus filter, the anchors are formed from the strut itself.

[0015] When anchor members are attached by a sacrificial link, thematerial of the sacrificial link is selected to be one which issusceptible to electrolytic disintegration in blood. The thrombus filterincludes an insulating layer substantially covering the thrombus filterincluding the body portion, the struts and the anchor members. Anopening in the insulation layer is selectively created over a portion ofthe thrombus filter which retains anchors to the free ends of thestruts. This opening in the insulating layer allows direct contactbetween the material of the thrombus filter and the patient's blood.This direct contact creates a conductive path between a portion of thethrombus filter and the patient's blood.

[0016] When removal of the thrombus filter is desired, a removalcatheter with a lumen and a distal end is disposed in the lumen of theblood vessel. The removal catheter enters the patient's vascular systemat a point which is readily accessible to the physician. Once in thevascular system, the catheter is urged forward until the distal end ofthe removal catheter is proximate the thrombus filter. A firstelectrical conductor is disposed inside the lumen of the removalcatheter. The first electrical conductor includes a proximal end and adistal end. The distal end of the first electrical connector penetratesthe insulating layer on the thrombus filter to form an electricalconnection with the body portion of the thrombus filter. The proximalend of the first electrical conductor is electrically connected to apower supply. A proximal end of the second electrical conductor is alsoelectrically connected to the power supply. The distal end of the secondelectrical conductor is electrically connected to the body of thepatient.

[0017] The power supply is used to selectively apply a voltagedifferential between the first electrical conductor and the secondelectrical conductor. This voltage differential induces a current flowbetween the thrombus filter and the blood of the patient. Because thethrombus filter is covered with an insulating layer, this current mustflow through the area proximate the opening in the insulating layer. Theflow of current causes electrolytic corrosion of the thrombus filter inthe selected area. The flow of electrical current between the thrombusfilter and the patient's blood is continued until a selected portion ofthe thrombus filter has been weakened or cut completely free byelectrolytic corrosion. The weakened link will separate when a load isapplied, for example, by an elongated pulling tool.

[0018] When the anchor portions of the thrombus filter are separated inthis fashion, the thrombus filter may be pulled into the lumen of theretrieval catheter leaving the anchor portions attached to the bloodvessel wall. Pulling the thrombus filter into the lumen of the retrievalcatheter causes the struts to collapse. When the struts collapse, thethrombus filter is transformed from a generally conical shape to agenerally cylindrical shape. Pulling of the thrombus filter into thelumen of the retrieval catheter may be accomplished with a retrievalwire including a hook. The anchor members remain fixed in the walls ofthe blood vessel by encapsulating cell growth due to neointimalhyperplasia. When the thrombus filter is pulled into the lumen of theretrieval catheter, the removal of the thrombus filter from the patientbecomes simply a matter of withdrawing the removal catheter from thelumen of the blood vessel.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019]FIG. 1 is a perspective view of a thrombus filter;

[0020]FIG. 2 is a plan view of a portion of the thrombus filterincluding an anchor portion and a weakened strut portion;

[0021]FIG. 3 is a plan view of a portion of a thrombus filter includingan anchor portion and a weakened strut portion;

[0022]FIG. 4 is a plan view of a portion of a thrombus filter includingan anchor portion and a weakened strut portion;

[0023]FIG. 5 is a plan view of a portion of a thrombus filterillustrating attachment of an anchor portion to a strut portion;

[0024]FIG. 6 is a schematic representation of the removal of a thrombusfilter from a blood vessel;

[0025]FIG. 7 is a schematic illustration of a thrombus filter which hasbeen pulled into the lumen of a retrieval catheter; and

[0026]FIG. 8 is a plan view of a portion of the thrombus filter.

DETAILED DESCRIPTION OF THE INVENTION

[0027]FIG. 1 is a perspective view of a thrombus filter 20. Thrombusfilter 20 includes a body member 22 and a plurality of elongated struts24. Struts 24 each have a joined end 26 and a free end 28. Joined end 26of each strut 24 is fixedly attached to body member 22.

[0028] Struts 24 may be fabricated from wire with a circular orrectangular cross section. For example, struts 24 may be comprised of 2inch lengths of 0.018″ diameter wire. Stainless steel, titanium, andnickel-titanium alloys have all been found to be acceptable materialsfor struts 24. In the embodiment of FIG. 1, a plurality of bends 25 aredisposed between free end 28 and fixed end 26 of each strut 24. Itshould be understood that struts 24 may also be straight, or includebends different than those illustrated in FIG. 1, without departing fromthe spirit or scope of the present invention.

[0029] In the embodiment of FIG. 1, body member 22 is generallycylindrical in shape, and includes a bore 23. It should be understoodthat other embodiments of body member 22 are possible without departingfrom the spirit or scope of the present invention.

[0030] Struts 24 radiate outwardly from body member 22 such thatthrombus filter 20 is generally conical in shape. When thrombus filter20 is deployed inside a blood vessel, free ends 28 engage the bloodvessel wall. Body member 22 is held in a position proximate to thecenter of the blood vessel by the plurality of struts 24 which engagethe blood vessel walls with opposing force vectors.

[0031] When thrombus filter 20 is disposed in a blood vessel, theconical formation of struts 24 acts to trap, or capture blood clots. Thegenerally conical shape of the formation of struts 24 serves to urgecaptured blood clots toward the center of the blood flow. The flow ofblood around the captured blood clots allows the body's natural lysingprocess to dissolve the clots.

[0032] To assure firm attachment of thrombus filter 20 to the bloodvessel, anchor members may be attached to free ends 28 of struts 24.FIG. 2 illustrates one embodiment of an anchor member 30 including astem 32 and a sharp projection 34. Stem 32 of anchor member 30 isattached to strut 24 with a sleeve 36.

[0033] In FIG. 2, sleeve 36 is fixedly attached to free end 28 of strut24 with a weld joint 38. Other methods of attachment may be used withoutdeparting from the spirit or scope of this invention. For example,sleeve 36 may be fixedly attached to free end 28 of strut 24 throughsoldering, brazing, crimping, or swaging. Sleeve 36 could also beattached to strut 24 with a fastening means such as a suture. Finally,sleeve 36 could be bonded to strut 24 with a permanent adhesive.

[0034] Stem 32 is adapted to releasably mate with sleeve 36. The methodof connecting stem 32 to sleeve 36 is selected so that the mechanicalstrength of the connection between sleeve 36 and stem 32 will be lessthan the mechanical strength of the connection between sleeve 36 andstrut 24. Several methods of accomplishing this releasable connectionhave been contemplated. For example, the outer diameter of stem 32 andthe inside diameter of sleeve 36 may be selected to form an interferencefit. In another embodiment of the present invention, an adhesive may beused to attach stem 32 to sleeve 36, this adhesive would be selected sothat the connection between stem 32 and sleeve 36 would be weaker thanthe connection between strut 24 and sleeve 36.

[0035] When thrombus filter 20 is removed from the body an extractioncatheter including an elongated pulling tool is used to exert a pullingforce on thrombus filter 20. Thrombus filter 20 is pulled with a forcewhich is sufficient to separate stem 32 from sleeve 36. Thereby removingthrombus filter 20 from the blood vessel, but leaving anchor members 30attached to the blood vessel wall.

[0036]FIG. 3 illustrates an alternate embodiment of the presentinvention. An anchor member 30 includes a stem 32 and a sharp projection34. Stem 32 of anchor member 30 is attached to free end 28 of strut 24with a sacrificial link 40 which is comprised of a material which issusceptible to electrolytic disintegration/weakening in blood.Sacrificial link 40 includes a first bore 42 and a second bore 44.

[0037] In the embodiment illustrated in FIG. 3, a first interference fitis formed between stem 32 of anchor member 30 and first bore 42 ofsacrificial link 40. A second interference fit may also be formedbetween free end 28 of strut 24 and second bore 44 of sacrificial link40. Alternately, free end 28 of strut 24 may be attached to sacrificiallink 40 using other methods. For example, sacrificial link 40 may befixedly attached to free end 28 of strut 24 through soldering, brazing,crimping, or swaging. Sacrificial link could also be attached to strut24 with a fastening means such as a suture. Finally, sacrificial link 40could be bonded to strut 24 with an adhesive.

[0038] In FIG. 3 it can be appreciated that thrombus filter 20 can beformed from the struts 24 shown in FIG. 3 as an alternative to thoseshown in FIG. 2. This alternative embodiment of thrombus filter 20 caninclude an insulating layer 39 substantially covering thrombus filter 20including body portion 22, struts 24, and anchor members 30 (thrombusfilter 20 and body portion 22 not shown in FIG. 3). In FIG. 3,insulating layer 39 is shown covering strut 24, anchor member 30, and aportion of sacrificial link 40. Insulation layer 39 includes an opening41 proximate sacrificial link 40. Opening 41 of insulating layer 39allows direct contact between sacrificial link 40 and the patientsblood. This direct contact creates a conductive path between sacrificiallink 40 and the body of the patient. The significance of this conductivepath will be described below.

[0039] A number of materials are suitable for use in insulating layer39, these materials include fluoropolytetrafluoroethylene (PTFE),polyethylene(PE), polypropylene (PP), polyvinylchloride (PVC), andpolyurethane. A number of manufacturing processes may be used to createinsulating layer 39. For example, a portion of insulating layer 39 maybe made up of sections of shrink tubing. The shrink tubing sections maybe positioned over the struts then shrunk by the application of heat. Aspray process may also be used to apply insulating layer 39 to thrombusfilter 20. For example, spraying PTFE solids in a suitable solventcarrier is a process which has been found suitable for this application.

[0040] Another material which may be used to fabricate insulating layer39 is a thermoplastic generically known as parylene. There are a varietyof polymers based on para-xylylene. These polymers are typically placedonto a substrate by vapor phase polymerization of the monomer. ParyleneN coatings are produced by vaporization of a di(P-xylylene)dimer,pyrollization, and condensation of the vapor to produce a polymer thatis maintained at comparatively lower temperature. In addition toparylene-N, parylene-C is derived from di(monochloro-P-xylylene) andparylene-D is derived from di(dichloro-P-xylylene). There are a varietyof known ways to apply parylene to substrates. The use of paralene insurgical devices has been disclosed in U.S. Pat. No. 5,380,320 (to J. R.Morris), in U.S. Pat. No. 5,174,295 (to Christian et al.), and in U.S.Pat. No. 6,067,491 (to Taylor et al.).

[0041]FIG. 4 illustrates an additional embodiment of the presentinvention. In this embodiment, a distal end 52 of stem 32 is positionedadjacent to free end 28 of strut 24 in a butt joint configuration.Distal end 52 of stem 32 is fixedly joined to free end 28 of strut 24with a sacrificial link 50. Sacrificial link 50 may be created using aprocess similar to brazing or soldering. The filler metal used in thisprocess would be one selected because it is susceptible to electrolyticdisintegration/weakening in blood.

[0042] In FIG. 4 it can be appreciated that thrombus filter 20 can beformed from the struts 24 shown in FIG. 4 as an alternative to thoseshown in FIG. 2. This alternative embodiment of thrombus filter 20 caninclude an insulating layer 39 substantially covering thrombus filter 20including body portion 22, struts 24, and anchor members 30 (thrombusfilter 20 and body portion 22 not shown in FIG. 4) In FIG. 4, insulatinglayer 39 is shown covering strut 24, anchor member 30, and a portion ofsacrificial link 50. Insulation layer 39 includes opening 51 proximatesacrificial link 50. Opening 51 of insulating layer 39 allows directcontact between sacrificial link 50 and the patient's body.Specifically, blood and tissue of the patients body is free to contactsacrificial link 50. This direct contact creates a conductive pathbetween sacrificial link 50 and the body of the patient.

[0043]FIG. 5 illustrates an additional embodiment of the presentinvention. In this embodiment, stem 32 of anchor 30 is positionedparallel to strut 24 in a lap joint configuration. Stem 32 of anchormember 30 is fixedly joined to strut 24 by a sacrificial link 60. As inthe previous embodiment, sacrificial link 60 may be created using aprocess similar to brazing or soldering. The filler metal used in thisprocess would be one which is susceptible to electrolyticdisintegration/weakening in blood.

[0044] In FIG. 5 it can be appreciated that thrombus filter 20 can beformed from the struts 24 shown in FIG. 5 as an alternative to thoseshown in FIG. 2. This alternative embodiment of thrombus filter 20 caninclude an insulating layer 39 substantially covering thrombus filter 20including body portion 22, struts 24, and anchor members 30 (thrombusfilter 20 and body portion 22 not shown in FIG. 5) In FIG. 5, insulatinglayer 39 is shown covering strut 24, anchor member 30, and a portion ofsacrificial link 60. Insulation layer 39 includes opening 61 proximatesacrificial link 60. Opening 61 of insulating layer 39 allows directcontact between sacrificial link 60 and the patient's blood. This directcontact creates a conductive path between sacrificial link 60 and thebody of the patient. The significance of this conductive path isdescribed in the following paragraph.

[0045] The embodiments shown in FIGS. 3, 4, and 5 include a sacrificiallink comprised of a material which is susceptible to electrolyticdisintegration/weakening in blood. When it is desirable to removethrombus filter 20 from a blood vessel, an electrical current is passedthrough sacrificial links 40, 50, 60. This electrical current causessacrificial links 40,50, 60 to corrode, dissolve, or disintegrate untilthe bond between free end 28 of strut 24 and stem 32 of anchor 30 isbroken or weakened.

[0046]FIG. 6 schematically illustrates a thrombus filter 20 disposed ina lumen 102 of blood vessel 100. As described previously, joined ends 26of struts 24 are fixedly joined to body portion 22. Free ends 28 ofstruts 24 are fixedly attached to anchors 30 by sacrificial links 60.

[0047] Blood vessel 100 includes walls 104 having a thin inner membraneor intima 106. Anchors 30 have punctured inner membrane 106 and areembedded in walls 104 of blood vessel 100. The body responds to thepuncturing of inner membrane 106 with a process referred to asneointimal hyperplasia. The punctured area of inner membrane 106 isovergrown with a multitude of new cells. In FIG. 6, these new cells areillustrated as encapsulating cell growth 108. Within about 2 to 3 weeksafter a thrombus filter is implanted, anchors 30 will be completelyencapsulated by encapsulating cell growth 108. With many prior artthrombus filters, removal of the filter after neointimal hyperplasiaencapsulation has occurred is very difficult, if not impossible.

[0048] A preferred embodiment of the thrombus filter in accordance withthe present invention can be removed using minimally invasive methodswithout complications due to neointimal hyperplasia of anchors 30. Aminimally invasive process which may be used to remove thrombus filter20 from blood vessel 100 is schematically represented in FIG. 6.

[0049] A removal catheter 110 with a lumen 112 and a distal end 114 isdisposed in lumen 102 of blood vessel 100. Removal catheter 110 entersthe patients vascular system at a point which is readily accessible tothe physician. Once in the vascular system, catheter 110 is urgedforward until distal end 114 is proximate to the thrombus filter 20.

[0050] A first electrical conductor 115 is disposed inside lumen 112of-removal catheter 110. First electrical conductor 115 includes aproximal end 116 and a distal end 118. Distal end 118 of firstelectrical conductor 115 has penetrated insulating layer 39 (not shown)to form an electrical connection with body portion 22 of thrombus filter20. Proximal end 116 of first electrical conductor 115 is electricallyconnected to a power supply 120. A proximal end 122 of a secondelectrical conductor is also electrically connected to power supply 120.A distal end 126 of second electrical conductor 124 is electricallyconnected to an area of exposed skin 128 of a living being. Theconnection between second electrical conductor 124 and skin 128 ispreferably made via an electrode 130.

[0051] A number of methods suitable for forming the electricalconnection between first electrical connector 114 and body portion 22 ofthrombus filter 20 are known in the art. For example, a needle electrodecould be disposed at distal end 118 of electrical connector 114. Theneedle electrode could penetrate insulating layer 39 and make electricalcontact with body portion 22 of thrombus filter 20. An easily deformedmaterial such as silicone rubber or silicone foam rubber could bedisposed around the needle electrode to insulate the electricalconnection.

[0052] Power supply 120 is used to selectively apply a voltagedifferential between first electrical conductor 114 and secondelectrical conductor 124. This voltage differential induces a currentflow 200 through sacrificial links 60 (links 40 and 50 could besacrificed in this manner as well). In FIG. 6, the path which currentflow 200 takes through the body of the patient is represented by adashed link. Current flow 200 causes sacrificial links 60 to corrode,dissolve, or disintegrate until the bond between free end 28 of strut 24and stem 32 of anchor 30 are broken or weakened. When the bonds betweenstruts 24 and anchors 30 is broken or weakened, thrombus filter 20 maybe pulled into lumen 112 of retrieval catheter 110.

[0053]FIG. 7 is a schematic representation of thrombus filter 20 afterit has been pulled into lumen 112 of retrieval catheter 110. As may beseen in FIG. 7, pulling thrombus filter 20 into lumen 112 of retrievalcatheter 110 causes struts 24 to collapse. When struts 24 collapsethrombus filter 20 is transformed from a generally conical shape to agenerally cylindrical shape. The pulling of thrombus filter 20 intolumen 112 of retrieval catheter 110 may be accomplished with a retrievalwire 140 including a hook 142. As can also be seen in FIG. 7, anchormembers 30 remain fixed in the walls of blood vessel 100 byencapsulating cell growth 108. When thrombus filter 20 is pulled intolumen 112 of retrieval catheter 110, the removal of thrombus filter 20from the patient becomes a simple matter of withdrawing removal catheter110 from lumen 102 of blood vessel 100.

[0054]FIG. 8 illustrates an additional embodiment of the presentinvention. In this embodiment, free end 28 of strut 24 includes a bend80 and a sharp projection 84. Bend 80 and sharp projection 84 enablefree end 28 of strut 24 to anchor thrombus filter 20 into the walls of ablood vessel. Strut 24 substantially covered with a layer of insulatingmaterial 39. A thrombus filter 20 of the embodiment shown in FIG. 8includes an insulating layer 39 substantially covering thrombus filter20 including body portion 22 (not shown) and struts 24. Insulation layer39 includes an opening 82 proximate free end 28 of strut 24. Opening 82of insulating layer 39 allows direct contact between strut 24 and thepatient's blood. This direct contact creates a conductive path betweenstrut 24 and the body of the patient.

[0055] The embodiment of FIG. 8 may be removed using a process similarto that shown in FIG. 6. A first electrical conductor forms anelectrical connection with the body portion of the thrombus filter. Asecond electrical conductor forms an electrical connection with thepatient's body. This connection may be via an electrode placed on thepatient's skin as shown in FIG. 6. It should be understood that theelectrical connection to the patient's body may be accomplished usingother methods without departing from the spirit or scope of theinvention. For example, the connection to the patients body may be madethrough an electrode disposed on the retrieval catheter which makesdirect contact with the patient's blood.

[0056] A power supply is used to selectively apply a voltagedifferential between the body portion of the thrombus filter and body ofthe patient. This voltage differential induces a current flow throughthe thrombus filter. In the embodiment of FIG. 8, current flows betweenstrut 24 and opening 82 in insulating layer 39.

[0057] The flow of electrical current between strut 24 and the patientsblood causes the electrolytic corrosion of strut 24 in an area proximateopening 82 in insulating layer 39. The current flow is continued untilstrut 24 has been weakened or cut through by electrolytic corrosion. Toreduce the time required for the removal of thrombus filter 20, thecross sectional area of strut 24 may be reduced proximate opening 82 ininsulating layer 39. When struts 24 of thrombus filter 20 are weakenedor cut through, thrombus filter 20 may be pulled into a retrievalcatheter.

[0058] Numerous advantages of the invention covered by this documenthave been set forth in the foregoing description. It will be understood,however, that this disclosure is, in many respects, only illustrative.Changes may be made in details, particularly in matters of shape, size,and arrangement of parts without exceeding the scope of the invention.The invention's scope is, of course, defined in the language in whichthe appended claims are expressed.

What is claimed is:
 1. A thrombus filter configured for placement withina blood vessel lumen defined by a blood vessel wall, comprising: a bodyportion; a plurality of struts, each strut having a joined end and afree end; the joined end of each strut being fixedly attached to thebody portion; and an anchor member joined to the free end of each strutby a sacrificial link.
 2. The thrombus filter of claim 1 , wherein eachanchor member includes a sharp projection.
 3. The thrombus filter ofclaim 1 , wherein the sacrificial link is susceptible to electrolyticweakening in blood.
 4. The thrombus filter of claim 1 wherein aninsulating layer is axially disposed about the struts.
 5. The thrombusfilter of claim 1 , wherein an insulating layer is selectively disposedabout the body portion.
 6. The thrombus filter of claim 1 , wherein eachstrut is rectangular in cross section.
 7. The thrombus filter of claim 1, wherein each strut is circular in cross section.
 8. A thrombus filterconfigured for placement within a blood vessel lumen defined by a bloodvessel wall, comprising: a body portion; a plurality of struts, eachstrut having a joined end and a free end; the joined end of each strutbeing fixedly attached to the body portion; an anchor member including asharp projection and a stem; and means for attaching the anchor memberto the free end of the strut by interference fit.
 9. The thrombus filterof claim 8 , wherein the struts have a circular cross section.
 10. Thethrombus filter of claim 8 , wherein the sleeves have a tubular crosssection, and the stems of the anchors have a circular cross section. 11.The thrombus filter of claim 8 , wherein the struts have a rectangularcross section.
 12. The thrombus filter of claim 8 , wherein the meansfor attaching includes a sleeve.
 13. The thrombus filter of claim 12 ,wherein each sleeve is attached to each strut with a weld joint.
 14. Thethrombus filter of claim 12 , wherein each sleeve is attached to eachstrut with a solder joint.
 15. A method of removing a thrombus filterfrom a blood vessel lumen inside a living being, the method comprisingthe steps of: providing a thrombus filter comprising, a body portion, aplurality of struts, each strut having a joined end and a free end, thejoined end of each strut being fixedly attached to the body portion, andan anchor member joined to the free end of each strut by a sacrificiallink; connecting a first electrical conductor to the body portion of thethrombus filter; connecting a second electrical conductor to the livingbeing; and creating a voltage differential between the first electricalconductor and the second electrical conductor whereby the sacrificiallinks are dissolved by electrolytic corrosion.
 16. The method of claim15 , wherein each anchor member includes a sharp projection.
 17. Themethod of claim 15 , wherein the sacrificial link is susceptible toelectrolytic weakening in blood.
 18. The method of claim 15 , wherein aninsulating layer is axially disposed about the struts.
 19. The method ofclaim 15 , wherein an insulating layer is selectively disposed about thebody portion.